Remove old gcc 4.6-4.7 from regression tests

Author: igaztanaga

.github/workflows/ci.yml

@@ -26,26 +26,6 @@ jobs:
           #------------------
           # Linux, gcc
           #------------------
-          # Linux, gcc-4.6
-          - toolset: gcc-4.6
-            cxxstd: "03,0x"
-            cxxflags: -pipe
-            address-model: 32,64
-            os: ubuntu-latest
-            container: ubuntu:16.04
-            install:
-              - g++-4.6-multilib
-            sources:
-              - "ppa:ubuntu-toolchain-r/test"
-          # Linux, gcc-4.7
-          - toolset: gcc-4.7
-            cxxstd: "03,11"
-            cxxflags: -pipe
-            address-model: 32,64
-            os: ubuntu-latest
-            container: ubuntu:16.04
-            install:
-              - g++-4.7-multilib
           # Linux, gcc-4.8
           - toolset: gcc-4.8
             cxxstd: "03,11"